For input devices, the keyboard is now the most widespread in use. In order to reduce manufacture costs and to simplify product design, the membrane keyboard spent lower cost and including a matrix circuit board gradually replaces the mechanical keyboard spent higher cost.
Generally, a situation associated with ghost keys may occur in the membrane keyboard using a matrix circuit board. Assume that the matrix circuit board includes two x-axis circuits, i.e. an upper x-axis circuit and a lower x-axis circuit, and two y-axis circuits crossing the two x-axis circuits, i.e. an upper y-axis circuit and a lower y-axis circuit, to form a square. Four nodes of the square respectively correspond to an upper left key, a lower left key, an upper right key and a lower right key sorted clockwise. When the upper left key, the lower left key and the upper right key are pressed simultaneously, the lower right key will be regarded as being pressed. Herein, four signals respectively specifying these keys are generated even though the upper right key is not pressed actually. This is called a ghost key phenomenon in the art.
Two solutions for avoiding the ghost key phenomenon have been used so far. One is to use firmware. The other one is to dispose a diode at each node to detect whether any ghost key occurs. However, using firmware may make the input of all keys failed to result in the word leakage when the ghost key phenomenon occurs, and disposing diodes may increase manufacturing costs. Therefore, it is necessary to have other solutions for avoiding the ghost key phenomenon.